1. Field of the Invention
The present invention relates to a disk-type magnetic recording/reproducing apparatus which can be used as a storage apparatus of a computer or as a storage apparatus for storing audio and video information.
2. Description of the Related Art
A motor employed in a tape-type magnetic recording/reproducing apparatus as a rotation driving means is designed into a mechanism wherein the characteristic of the motor can be switched from a low speed to a high speed in dependence on some types of rotation mode. In the case of a portable tape recorder, for example, one motor is used to drive a tape to travel at a low speed in a reproduction (playback) or recording operation and at a high speed in a fast-feed or rewind operation in neither a recording mode nor a reproduction mode. In order to implement the function to drive a tape at different speeds as described above, there is adopted a method whereby the characteristic of the motor is switched from a constant-speed (low-speed) state to a high-speed state and vice versa so as to allow the driven tape to travel well as is generally known.
In general, a disk-type magnetic recording/reproducing apparatus such as an apparatus for driving a floppy or hard disk used as an external storage device of a personal computer adopts a CAV (Constant Angular Velocity) system wherein the rotational angular velocity of a spindle motor serving as a rotation driving means is fixed.
In the case of a floppy disk, some floppy-disk drives adopt a CLV (Constant Linear Velocity) system wherein the rotational speed is varied from track to track to result in a fixed scanning velocity independently of the radial position of the head. The CAV and CLV systems are different from each other in that, in the case of the former, the scanning speed of the head is fixed while, in the case of the latter, the scanning speed of the head is variable. In the case of both the systems, however, only a single performance can be displayed as an operating mode allowing recording/reproduction operations.
It should be noted that, in the case of the CLV system, the ratio of a maximum rotational speed to a minimum rotational speed of a disk is equal the ratio of the radius of an outermost circumference of a data area on the disk for recording data to be reproduced later to the radius of an innermost circumference of the data area. That is, if the ratio of the outer-circumference radius to the inner-circumference radius of the data area is 2, the ratio of a maximum rotational speed to a minimum rotational speed of a disk is also 2. However, changes to rotational speed are controlled by a means for making the scanning speed of the head relative to the disk medium fixed and there is displayed only one recording/reproduction performance in a constant-speed recording/reproduction operating mode. That is, even if the rotational speed is changed, the recording/reproduction operating mode does not produce different kinds of recording/reproduction performance.
As such, in the prior art, there is no disk-type magnetic recording/reproduction apparatus which has a recording/reproduction operating mode providing different kinds of recording/reproduction performance at more than one rotational speed.
First of all, consider a hard-disk drive, a representative disk-type magnetic recording/reproduction apparatus. There are two kinds of hard-disk drive with a constant rotational speed: a hard-disk drive with a low rotational speed referred to hereafter as a low-speed disk drive and a hard-disk drive with a high rotational speed referred to hereafter as a high-speed disk drive. Differences between the low-speed disk drive and the high-speed disk drive are explained as follows.
The low-speed disk drive has an excellent power-consumption characteristic and an excellent rise time from a sleep mode in an operation to read a TOC (Table of Contents) or a FAT (File Allocation Table) used as an area for controlling data recording in files. That is, the rise time that results with the power consumed by the motor kept constant can be shortened and a motor cost for making the rise-time speed fixed as well as the amount of consumed power can be reduced.
On the other hand, the high-speed disk drive has an excellent capability of transferring data at a high transfer speed due to the fact that the disk is rotated at a high rotational speed.
Thus, a low-speed disk drive is not so good as a high-speed disk drive in that data can not be transferred at a high speed. However, the low-speed disk drive is convenient in that it can be employed in a portable apparatus due to the fact that the low-disk drive can be implemented with low power consumption. In addition, since it is difficult to implement a high-speed disk drive at low power consumption, the high-speed disk drive is not appropriate for a portable application wherein a long life of the battery thereof is desired. Nevertheless, the high-speed disk drive is capable of transferring data at a high speed.